Diaryl phosphate morpholinium salts

ABSTRACT

A membrane for use in the determination of calcium ion concentration in an aqueous solution, the membrane being of the type comprising a calcium ion selective component and a carrier material. The membrane is characterized in that the calcium ion selective component is a compound having a formula (I) ##STR1## wherein X and Y are independently selected from a group consisting of aryl, alkyl(aryl), alkenyl(aryl), alkynyl(aryl), alkyl, cycloalkyl, alkenyl, cycloalkenyl, and alkynyl radicals wherein said alkyl moiety of said alkyl(aryl) radical consists of 1-12 carbon atoms; each alkenyl and alkynyl moiety of said alkenyl(aryl) and alkynyl(aryl) radicals, respectively, consists of 2-12 carbon atoms; each aryl moiety consists of 6, 10, 12, or 14 carbon atoms; and each alkyl, cycloalkyl, alkenyl, cycloalkenyl, and alkynyl radical consists of 6 to 14 carbon atoms; and 
     Z is selected from a group consisting of alkyl radicals containing 1-12 carbon atoms; alkenyl and alkynyl radicals containing 4-12 carbon atoms; and cycloalkyl and cycloalkenyl radicals containing 6 to 12 carbon atoms. 
     The membrane can be employed in an electrode system. 
     A novel compound of formula I, supra, and a method for the manufacture thereof.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a division of application Ser. No. 107,031 filed Dec. 26, 1979now U.S. Pat. No. 4,271,002 which is a continuation-in-part of Ser. No.52,639 filed June 27, 1979, now U.S. Pat. No. 4,276,141 which is acontinuation in part of Ser. No. 880,908 filed Feb. 24, 1978, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a calcium ion-selective electrode and to acalcium ion-selective membrane for use therein.

2. Description of the Prior Art

Extensive research has been undertaken in the area of calciumion-selective electrodes as evidenced by the extensive patent (5-10) andtechnical (11-30) literature in this area and the development and stateof the art with respect to these electrodes has been documented (1-4).

More specifically, U.S. Pat. No. 3,729,401 (8) discloses the use of thediester of t-octylphenyl phosphoric acid as the calcium ion selectordissolved in an organic liquid such as di-n-octylphenylphosphonate. U.S.Pat. No. 3,932,233 (10) is directed to the calcium salts ofdi-(aryl)phosphates and di(n-alkylaryl) phosphates in admixture withtheir respective acid phosphates and combined with polyvinyl chlorideand di-n-octyl phenylphosphonate. Griffiths et al. (13) formed a solidmembrane system using polyvinyl chloride. Griffiths et al. (13) foundthat there was an optimum mixture in formulating the calcium membranewhen monocalcium dihydrogen tetra(didecylphosphate) was used in a weightratio of 1:10 with di-n-octyl phenylphosphonate plasticizer. This lattermixture was used in 71.2% concentrations by weight with 28.8% polyvinylchloride homopolymer added. The calcium acid tetra salt of the diesterphosphate was made up by mixing equal portions of the diester acidphosphate with monocalcium di(didecylphosphate). The work of Griffithset al. (13) was classic in calcium ion electrode technology and has beencopied by many workers in the art. Thus, it is considered necessary bythose skilled in the art to incorporate the ion sensing phosphate ligandas a calcium acid salt form into the plasticized membrane. Hence, allpurifications of the diester phosphates have involved the isolation ofboth the diester acid phosphate and the calcium salt diester phosphateand then combining the two equivalent ingredients into the phosphonateplasticizer in the 1:10 ratio.

Recently, Moody et al. (30) have disclosed that one can obtainsatisfactory results using just the calcium salt ofbis[di(p-1,1,2,2-tetramethylbutylphenyl) phosphate] in conjunction witha plasticizer in a ratio of up to 1 part calcium salt to 10 partsplasticizer.

However, serious shortcomings exist with the prior art calciumelectrodes. These shortcomings include (1) a relatively slow response ofthe calcium electrode; (2) a relatively poor selectivity to calcium inthe lower ion concentration ranges; (3) a relatively poor use life; and(4) a relatively difficult manufacturing process entailed in themanufacture thereof.

It would therefore be very advantageous to have a calcium electrode andmembrane for use therein which overcomes these problems present in theprior art.

SUMMARY OF THE INVENTION

In accordance with the present invention there are provided a calciumion electrode and a calcium ion-selective membrane for use therein whichpossesses (1) a fast response to calcium ion concentrations, (2) anexcellent selectivity to calcium in the lower ion concentration ranges;(3) an extended use life; and (4) a simplified manufacturing process inthe production thereof.

More particularly, the membrane for use in the determination of calciumion concentration is of the type comprising a calcium ion-selectivecomponent and a carrier material. The membrane is characterized in thatthe calcium ion-selective component is a compound having a formula I##STR2## wherein X and Y are independently selected from a groupconsisting of aryl, alkyl(aryl), alkenyl(aryl), alkynyl(aryl), alkyl,cycloalkyl, alkenyl, cycloalkenyl and alkynyl radicals. The alkyl moietyof the alkyl(aryl) radical consists of 1-12 carbon atoms. Each alkenyland alkynyl moiety of the alkenyl(aryl) and alkynyl(aryl) radicals,respectively, consist of 2-12 carbon atoms. Each aryl moiety consists of6, 10, 12, or 14 carbon atoms; and each alkyl, cycloalkyl, alkenyl,cycloalkenyl, and alkynyl radical consists of 6-14 carbon atoms. Z isselected from a group consisting of alkyl radicals containing 1-12carbon atoms; alkenyl and alkynyl radicals containing 4-12 carbon atoms;and cycloalkyl and cycloalkenyl radicals containing 6-12 carbon atoms.

The improved electrode of the instant invention is of the typecomprising a membrane and means, including an electrode substrate, forsupporting the membrane. The improved electrode is characterized in thatthe above described membrane is employed therein.

Also encompassed within the scope of the present invention is thecompound of formula I, supra, and a method for the manufacture thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an electrode within the scope ofthe instant invention.

FIG. 2 is a schematic representation of a preferred solid stateelectrode within the scope of the instant invention.

FIG. 3 is a schematic representation of a solid state electrode withinthe scope of the instant invention.

FIG. 4 is a schematic representation of an ISEFET electrode within thescope of the instant invention.

FIG. 5 is a chart recording of a prior art electrode.

FIG. 6 is a chart recording of an electrode within the scope of theinstant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The membrane of the instant invention employed for use in thedetermination of calcium ion concentration is of the type comprising acalcium ion-selecting component and a carrier material. The membrane ischaracterized in that the calcium ion-selective component is a compoundhaving a formula I ##STR3## wherein X and Y are selected from a groupconsisting of aryl, alkyl(aryl), alkenyl(aryl), alkynyl(aryl), alkyl,cycloalkyl, alkenyl, cycloalkenyl, and alkynyl radicals. The alkylmoiety of the alkyl(aryl) radical consists of 1-12 carbon atoms. Eachalkenyl and alkynyl moiety of the alkenyl(aryl) and alkynyl(aryl)radicals, respectively, consists of 2-12 carbon atoms. Each aryl moietyconsists of 6, 10, 12, or 14 carbon atoms. Each alkyl, cycloalkyl,alkenyl, cycloalkenyl, and alkynyl radical consists of 6-14 carbonatoms. Z is selected from a group consisting of alkyl radicalscontaining 1-12 carbon atoms; alkenyl and alkynyl radicals containing4-12 carbon atoms; and cycloalkyl and cycloalkenyl radicals containing6-12 carbon atoms.

Preferably X and Y are the same.

Examples of akyl(aryl), alkenyl(aryl), and alkynyl(aryl) radicals whichcan be employed in the instant invention include, but are not limitedto, (t-butyl)phenyl, p-(t-butyl)diphenyl, (t-butyl)naphthyl,(n-octyl)phenyl, (iso-octyl)phenyl, (t-octyl)phenyl, (t-octyl)napthyl,(methyl)phenyl, (ethyl)phenyl, (n-propyl)phenyl, (iso-propyl)phenyl,(n-butyl)phenyl, (iso-butyl)phenyl, (n-pentyl)phenyl, (n-hexyl)phenyl,(1,2-dimethylbutyl)phenyl, (2-ethylhexyl)phenyl, (iso-nonyl)phenyl,(n-decyl)phenyl, (iso-decyl)phenyl, and (n-dodecyl)phenyl. Alkyl(aryl)radicals which are derivatives of commercially available compoundsinclude p-(1,1,3,3-tetramethylbutyl)phenyl, p-(iso-decyl)phenyl,p-(n-decyl)phenyl, p-(2-ethylhexyl)phenyl and p-(n-octyl)phenyl.

Examples of alkyl, cycloalkyl, alkenyl, cycloalkenyl, and alkynylradicals which can be employed in the instant invention include, but arenot limited to, cyclohexyl, cyclooctyl, cyclooctenyl, octenyl-1,cyclododecyl, dodecenyl-1, t-butyl, 3-butynyl, n-octyl, iso-octyl,t-octyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,n-pentyl, n-hexyl, 1-heptynyl, 1,2-dimethylbutyl, 2-ethylhexyl,iso-nonyl, n-decyl, iso-decyl, and n-dodecyl. Preferred alkyl radicalsinclude n-octyl, isononyl, n-dodecyl, n-decyl, and iso-decyl.

Examples of alkyl, alkenyl, alkynyl, cycloalkyl, and cycloalkenylradicals which can be employed as Z in the instant invention include,but are not limited to, cyclohexyl, cyclooctyl, cyclooctenyl, octenyl-1,cyclododecyl, dodecenyl-1, t-butyl, n-octyl, t-octyl, methyl, ethyl,n-propyl, iso-propyl, n-butyl, 3-butenyl, sec-butyl, n-pentyl, n-hexyl,1-heptynyl, 1,2-dimethylbutyl, 2-ethylhexyl, n-decyl, and n-dodecyl.Preferably, Z is ethyl.

The calcium ion-selective component of formula I can be synthesized viathe following procedure. First, a compound having a formula II ##STR4##wherein X and Y are as defined above, is either prepared via any wellknown procedure, e.g., that exemplified in U.S. Pat. No. 3,932,233, orpurchased from a chemical supplier. The compound of formula II, whethermade or purchased, is usually present in a a mixture containing thedesired compound II and at least one reaction co-product selected from agroup consisting of ##STR5## wherein X and Y are as defined above andwherein E is selected from the same group from which X and Y areselected. Compound II can be separated from the above mixture via aseparation procedure which entails:

(a) mixing the mixture with a solvent selected from a group consistingof heptane, cyclohexane, and mixtures thereof;

(b) mixing ethylene glycol with the product of step (a);

(c) allowing the mixture of step (b) to form a hydrocarbon layer and anethylene glycol layer;

(d) separating the hydrocarbon layer from the ethylene glycol layer; and

(e) extracting the hydrocarbon layer at least once with water.

To the extracted hydrocarbon layer of step (e) is then added (as step f)a compound having the formula VI ##STR6## wherein Z is as defined above,thereby forming the compound of formula I.

This process can be done at any convenient temperature and is preferablyconducted at room temperature. Preferably, steps (b), (c), and (d) arerepeated 3 or more times and step (e) is repeated 2 or more times.Furthermore, to avoid the formation of colloids during the waterextraction step (e), slightly acidic water (i.e., water having a pHbelow 5.5, preferably from about 3 to about 5, and more preferably fromabout 4 to about 5) is desirable for use in step (e). It is alsopreferred that after step (e) and prior to step (f) the extractedhydrocarbon layer be contacted with a suitable neutral anhydrousdessicant, e.g., anhydrous sodium sulfate. The dessicant can be removedfrom the hydrocarbon layer via any convenient separation process, e.g.,filtration, to thereby obtain a dried hydrocarbon layer for use in step(f).

In the broadest sense of the instant invention, the carrier materialemployed in the membrane of the instant invention can be formulated fromany material which has been employed as a carrier material by thoseskilled in the art. In one preferred embodiment of the instantinvention, the carrier material employed in the membrane comprises afirst lipophilic-hydrophobic (LH) layer and a second LH layer inintimate contact with the first layer, the calcium ion-selectivecomponent being present in the second layer. The first LH layer cancomprise an adhesive, LH polymer having an intrinsic viscosity of fromabout 0.4 to about 0.9, preferably from about 0.5 to about 0.7, and morepreferably about 0.6, ml/g; and a LH plasticizer. The adhesive, LHpolymer is preferably selected from a group consisting of halogenatedand unhalogenated aliphatic, cycloaliphatic, and aromatic polymers,copolymers, and terpolymers, as well as block polymers and graphpolymers thereof. More preferably, the adhesive, LH polymer is selectedfrom a group consisting of polyurethane, polyvinyl chloride homopolymer,polyvinyl chloride-ethylene copolymer, polyvinyl chloride-propylenecopolymer, polyvinyl chloride-butylene copolymer, polyvinylchloride-ethylhexene copolymer, polyvinyl chloride-isoprene copolymer,polyvinyl chloride-butadiene copolymer, polyvinyl chloride-vinyl toluenecopolymer, polyvinyl chloride-styrene copolymer, styrene-ethylenecopolymer, styrene-propylene copolymer, styrene-butylene copolymer,styrene-ethylhexene copolymer, styrene-isoprene copolymer,styrene-butadiene copolymer, and styrene-butadiene-acrylonitrileterpolymer. The adhesive, LH polymer to be employed in the first LHlayer for use in the determination of calcium ion concentration is morepreferably selected from the group consisting of polyvinylchloride-propylene copolymer and styrene-isoprene copolymer.

The LH plasticizer should be compatible in high concentrations with theabove described adhesive, LH polymer and should enhance the adhesivecharacteristics of the polymer. Preferably, the LH plasticizer isselected from a group consisting of adipates, ethers, phosphates,phosphonates, and mixtures thereof. More particularly, the LHplasticizer is selected from the group consisting of nitroaryl alkylethers, nitroaryl alkylaryl ethers, nitroaryl arylalkyl ethers,bis(nitroaryl)ethers, nitroaryl aryl ethers, dialkyl alkylphosphonates,dialkyl arylphosphonates, and diaryl arylphosphonates, diarylalkylphosphonates, trialkyl phosphates, trialkylaryl phosphates, triarylphosphates, triarylalkyl phosphates, mixtures thereof and at least oneof the above in admixture with at least one compound selected from agroup consisting of dialkyl adipates, dialkylaryl adipates, diaryladipates, and diarylalkyl adipates wherein each alkyl group containsfrom 8-14 carbon atoms and each aryl group contains from 6, 10, or 12carbon atoms. It is further preferred that each alkyl group contain from8-12 carbon atoms and be in the normal or iso-alkyl configuration.

More preferably, the plasticizer to be employed in the first LH layer isselected from the group consisting of dioctylphenyl phosphonate andtri(1,1,3,3-tetramethylbutyl)phosphate. Optimally the plasticizer isdi-n-octyl phenylphosphonate.

Overlaying the first LH layer and in intimate contact therewith is asecond LH layer. This second LH layer comprises an LH polymer having anintrinsic viscosity of from about 1 to about 1.5, preferably from 1 toabout 1.3, and more preferably about 1.1 to about 1.2 mg/l; an LHplasticizer; and a calcium ion-selective component.

The LH polymer should be of the type that remains strong and durableeven when highly plasticized. Preferably, this LH polymer is a polyvinylchloride homopolymer.

The LH plasticizer employed in the second layer should possess the samedesirable properties as described above with respect to the plasticizeremployed in the first LH layer. The preferred plasticizers employed inthe second LH layer are also the preferred plasticizer employed in thefirst LH layer. Furthermore, it is preferred that the same plasticizersbe employed in both the first LH layer and the second LH layer.

The ratio of the above described constituents present in the first LHlayer and the second LH layer is not critical. However, it is preferredthat the first LH layer comprise from about 10 to about 60, preferablyfrom about 15 to about 40, and optimally from about 15 to about 25,weight percent of the adhesive, LH polymer; from about 40 to about 90,more preferably from about 60 to about 85, and optimally about 75 toabout 85 weight percent of the LH plasticizer.

With respect to the second LH layer, this layer preferably comprisesfrom about 25 to about 60, more preferably from about 35 to about 45,and optimally about 42.5, weight percent of the LH polymer; from about30 to about 74.9, more preferably from about 55 to about 65, andoptimally about 55, weight percent of the LH plasticizer; and from about0.1 to about 10, more preferably from about 2 to about 6, and optimallyabout 2.5, weight percent of the calcium ion-selective component.

The dielectric constants of the first LH layer and the second LH layerare not critical. However, for the determination of calcium it ispreferred that the first and second LH layers have a dielectric constantof from about 5 to about 25 to 60 cycles.

The composition of the first LH layer can be prepared, in general, bymixing the adhesive, LH polymer and the LH plasticizer together. To themixture is added a solvent, such as a 50:50 by volumexylene:1,2-dichloroethane solution. This mixture should be thoroughlyand continuously mixed. If desired, one can heat the mixture to about50° C. to reduce the time required for complete mixing. The mixture isthen cooled to room temperature.

The composition of the second LH layer can be prepared, in general, bymixing the LH polymer and the plasticizer together and adding to themixture a solvent, such as cyclohexanone. This mixture should bethoroughly and continuously mixed. If desired, one can heat the mixtureto about 50° C. to reduce the time required for complete mixing. Whenthe mixture has cooled to room temperature, the calcium ion-selectivecomponent can be added to the mixture and the mixture again mixed. Thecalcium ion-selective component can be added as a solution wherein thesolvent is, for example, cyclohexanone.

In one preferred embodiment, the first LH layer of the membrane of thisinvention also comprises the above calcium ion-selective component. Insuch a case the membrane composition is prepared as discussed above andis added to the reaction mixture after the reaction mixture has cooledto room temperature and the mixture is again mixed. The calciumion-selective component can be added as a solution wherein the solventis, for example, cyclohexanone.

The ratio of the constituents present in a calcium ion-selectivecomponent containing first LH layer is not critical. However, it ispreferred that the calcium ion-selective component containing first LHlayer comprise from about 10 to about 60, preferably from about 12.5 toabout 40, and optimally from about 14.9 to about 25, weight percent ofthe adhesive, LH polymer; from about 35 to about 89.99, and morepreferably from about 59 to about 87, and optimally from about 74.5 toabout 85, weight percent of the LH plasticizer; and from about 0.01 toabout 5, more preferably from about 0.05 to about 1, and optimally, fromabout 0.1 to about 0.5, weight percent of the calcium ion-selectivecomponent.

The membrane of the instant invention can be employed in any electrodeknown to those skilled in the art. With respect to FIG. 1, a typicalelectrode comprises a membrane 1 and means 3, including an electrodesubstrate 7, for electrically connecting the membrane 1 with conductivelead 9, the electrode substrate being located within an insulating stem5. Examples of electrodes well known to those skilled in the artinclude, but are not limited to, liquid-junction electrodes, solid stateelectrodes, ion-selective electrode field effect transistor (ISEFET)electrodes and their corresponding microelectric embodiments.

A preferred solid state electrode embodiment of the instant invention isshown in FIG. 2. An electrically conductive element 6 is firmly held byan electrically insulating cap 8. The cap 8 has means 10 for holding anelectrically insulating stem 12 such that electrical conductor 14 is inelectrical communication with element 6. Conductor 14 is in electricalcommunication with electrically conductive lead 16. A first LH layer 2is in intimate contact with element 6 and a second LH layer 4 is inintimate contact with the first layer 2.

The lettered numbers of the solid state electrode of FIG. 3 depictanother embodiment of the corresponding numbered item discussed withrespect to FIG. 2 above. More particularly, a first LH layer 2a is inintimate contact with electrical conductor 14a and a second LH layer 4ais in intimate contact with first layer 2a. Conductor 14a is inelectrical communication with electrically conductive lead 16a and islocated with insulating stem 12a.

FIG. 4 depicts an ISEFET electrode embodiment of the instant invention.A p-type silicon substrate 20 has two n-type regions, a source diffusionregion 22 and a drain diffusion region 24, diffused into the surface ofthe substrate 20 to a depth, for example, of from one to two microns andspaced twenty microns apart. The ISEFET also includes a thin layer ofelectrical insulator material 26, such as silicon dioxide, depositedover the substrate 20 and portions of the diffusion regions 22 and 24.Conductive layers 30 and 32, such as aluminum, n-type silicon, etc., aredeposited respectively into the source diffusion region 22 and the draindiffusion region 24 to provide electrical contact therewith. A membrane28 is deposited over the insulator material 26 above the gate region ofthe ISEFET. Deposition of membrane 28 on the insulator material 26 maybe carried out simply by solution casting and may, illustratively, be ofa thickness of about 5 microns. Preferably, a layer (not shown) ofsilicon nitride is deposited between the insulator material 26 andmembrane 28 in gate region 27. Since the ISEFET of the instant inventionwould typically be immersed in or exposed to solutions containing thecalcium ion to be assayed, it is desirable that all of the membrane 28be covered with some type of solution impervious material except for aportion 29 of the membrane which is left exposed for contact with a testsolution. Layer 34 represents such material, for example, a polymerizedepoxy resin. Although the layer 34 in FIG. 4 is only shown as coveringthe insulator material 26 and a portion of the membrane 28, it should beunderstood that the solution impervious material would cover all partsof the device including electrical leads, etc., which might be immersedin the solution except for the exposed portion 29. The type of solutionimpervious material used, of course, would depend upon the kinds ofsolution into which the ISEFET is to be immersed, but generally, thematerial should be at least water impervious and preferablybiocompatible, i.e., should not adversely interact with the solution ortissue to which the device is exposed.

The electrodes of the instant invention can be fabricated in a number ofdifferent ways depending on a desired configuration as well as one'smanufacturing capabilities. For example, if a solid state electrode suchas shown in FIG. 2 is desired, the first LH layer is formed by placing apredetermined amount of the mixture of the composition of the firstlayer over element and drying the coated element at room temperature. Ifdesired, this sequence can be repeated more than once. Over the driedfirst layer is placed a predetermined amount of the mixture of thecomposition of the second layer and also dried at room temperature. Ifdesired, this latter sequence can also be repeated more than one time,and preferably is repeated at least once.

The electrodes within the scope of this invention can be employed todetermine calcium ion concentration in any suitable solution. Thesolution can, for example, be water, biological fluids, such as bloodand urine, aqueous solutions, such as wine and beer, and numerous otherliquids and environments wherein one desires to perform such endmeasurement.

The following examples are provided for the purpose of furtherillustration only and are not intended to be limitations on thedisclosed invention.

EXAMPLE 1 Synthesis of N-Ethyl-Morpholinium Salt of Dioctylphenyl AcidPhosphate

A. To a 500 ml separatory funnel was added via a powder funnel a weighedamount (about 40 gm) of octylphenyl acid phosphate from Mobil ChemicalCo. (reported to be a 70/30 mixture of the di/mono-esters ((RO)₂ POOHand (RO)PO(OH)₂, respectively, wherein R is C₈ H₁₇ C₆ H₄ --). Next, 200ml of dry heptane was added to the separatory funnel. the separatoryfunnel was then stoppered and shaken to dissolve the crude octylphenylphosphate. (A portion of the octylphenyl phosphate, thought to be themonoester phosphate, did not completely dissolve.)

B. To the contents present in the separatory funnel were then added 200ml ethylene glycol (c.p.). The separatory funnel was restoppered andshaken vigorously to extract the more glycol-soluble monoester phosphatefrom the diester phosphate (which remained in the heptane layer). Thetwo layers were allowed to completely separate and then the bottomglycol layer was drawn off.

C. A fresh portion (200 ml) of ethylene glycol was added to theseparatory funnel. The separatory funnel and its contents were shakenvigorously for several minutes and then allowed to stand until thelayers separated clearly. The glycol layer was once again carefullydrawn off.

D. Step C was repeated three more times.

E. To the separatory funnel was now added 150 ml of 0.1 M HCl. Theseparatory funnel and its contents were shaken vigorously and thenallowed to stand until the layers separated clearly. The acid layer wasdrawn off and this dilute acid wash step was repeated one more time.

F. After carefully removing all the aqueous acid from the heptane layerat the bottom of the separatory funnel, approximately 40 gms ofanhydrous sodium sulfate powder was added directly to the separatoryfunnel and the heptane contents. The heptane and sodium sulfate werevigorously mixed together for a few minutes and then allowed to stand(after relieving any internal pressure build-up) in the funnel foranother 10-15 minutes.

G. To remove all the sodium sulfate from the heptane, the heptane fromstep F was then poured from the top of the separatory funnel into amedium pore fritted glass Buchner funnel.

H. While stirring the dry filtered heptane, 10 ml of N-ethyl morpholinewas added. The stirring was continued for a few minutes after completeaddition of the N-ethyl morpholine. The container was covered andstirred for about an hour. A somewhat slow crystallization of thediester phosphate morpholinium quaternary salt formed and precipitatedover this period.

I. The white crystalline precipitate was filtered in a fritted Buchnerfunnel under vacuum and rinsed once with about 100 ml of chilled heptanethereafter.

J. The white precipitate was vacuum dried for several hours and thenplaced in an amber bottle and capped and weighed to determine the yieldof the diester product.

K. Calculations

40.87 g of Mobil brand Octylphenyl acid phosphate

22.06 g of dry white precipitate from (J) above ##EQU1## X=17.76 g offree diester actually isolated (as morpholineum salt)

The Mobil brand octylphenyl acid phosphate mixture is stated to be 70/30of diester to monoester. Thus, 40.87 g of mixture should yield40.87×0.7=28.6/g of free acid diester phosphate, therefore: ##EQU2##

EXAMPLE 2 Compounding of Composition for Layer 2 Devoid of CalciumIonophore

A. Flowell 470 brand polyvinyl chloride-propylene copolymer (1.8 gm) wasweighed out into a 60 ml of capacity wide mouth amber bottle equippedwith a polyseal cap.

B. Dioctyl phenylphosphonate (8.2 gm) was added to the polyvinylchloride-propylene copolymer and the two ingredients were then mixed,thereby forming a slurry.

C. Finally, 35 ml of a 50/50 by volume xylene/dichloroethane solvent wasadded to the above slurry.

D. The bottle was quickly closed and vigorously shaken and then placedon a roll mixer and continuously mixed under a 50° C. heat lamp untilall the ingredients had clearly dissolved.

EXAMPLE 3 Compounding of Another Composition for Layer 2 Devoid ofCalcium Ionophore

The procedure set forth in Example 2 was employed with the solemodification being the substitution of a 50/50 by volume (8.2 gm)mixture of dioctyl adipate and dioctyl phenylphosphonate for the 8.2 gmof dioctyl phenylphosphonate used therein.

EXAMPLE 4 Compounding a Calcium Ionophore Containing Composition ofLayer 2

The procedure set forth in Example 2 was employed with the followingmodifications:

1. 8.1 gm of dioctyl phenylphosphonate was employed instead of 8.2 gm;

2. After step B, 0.1 gm of N-ethyl-morpholinium salt of dioctylphenylphosphoric acid (EM.HDOPP) was added to the slurry formed in step B andthe resulting mixture thoroughly mixed.

EXAMPLE 5 Compounding Another Calcium Ionophore Containing Compositionfor Layer 2

The procedure set forth in Example 4 was employed with the solemodification being the substitution of a 50/50 by volume (8.1 gm)mixture of dioctyl adipate and dioctyl phenylphosphonate for the 8.1 gmof dioctyl phenylphosphonate used therein.

EXAMPLE 6 Compounding of Composition for Layer 4

A. Geon 102EPF5 brand polyvinyl chloride homopolymer (4.25 gm) wasweighed out into a 60 ml capacity wide mouth amber bottle equipped witha polyseal cap.

B. Dioctyl phenylphosphonate (5.5 gm) was added to the polyvinylchloride homopolymer and the two ingredients were then mixed therebyforming a slurry.

C. Next, 0.25 gm EM"DOPP was added to the above slurry and the resultingslurry-mixture thoroughly mixed.

D. Finally, 40 ml of cyclohexanone solvent was added to this slurrymixture.

E. The bottle was quickly closed and vigorously shaken and then placedon a roll mixer and continuously mixed under a 50° C. heat lamp untilall the ingredients had clearly dissolved.

EXAMPLE 7 Fabrication of Membrane

A cap of the type schematically shown in FIG. 2 as numeral 8 havingfirmly held therein an element comprising a compacted mixture ofsilver-silver chloride was selected. The composition (35 ml) prepared inExample 2 was then deposited over the element and allowed to dry at roomtemperature for about 24 hours. Next, 35 ml of the composition preparedin Example 6 was then deposited over the first layer and also allowed todry at room temperature for 24 hours. A second 35 ml aliquot of thecomposition prepared in Example 6 was deposited over the previouslydried layers and allowed to dry in air for an additional 72 hours.

EXAMPLE 8 Life Span

The solid state electrode prepared in Example 7 was evaluated forNernstian activity and the data obtained therefrom is shown in Table I.

                                      TABLE I                                     __________________________________________________________________________    ELECTRODE LIFE SPAN FOR CALCIUM ELECTRODE                                     Moles/Liter (M/l) vs. Millivoltage (mV)                                                                      Span (mV) per Decade                           Day                                                                              10.sup.-5 M/l                                                                      10.sup.-4 M/l                                                                       10.sup.-3 M/l                                                                       10.sup.-2 M/l                                                                       10.sup.-1 M/l                                                                      10.sup.-5 -10.sup.-4 M/l                                                              10.sup.-4 -10.sup.-3 M/l                                                              10.sup.-3 -10.sup.-2                                                                  10.sup.-2 -10.sup.-                                                           1 M/l                  __________________________________________________________________________    DATA FOR ELECTRODE WITHIN SCOPE OF INSTANT INVENTION (EXAMPLE 8)               1 -72  -45   -16   +12.5 +42  27      29      28.5    29.5                    2 -70  -41.5 -9.5  +22   +55  28.5    32      31.5    33                     162                                                                              -34  -5.5  +21.5 +56   +85  28.5    27      34.5    29                     367                                                                              -40  -9.5  +17.5 +44.5 +75  30.5    27      27      30.5                   382                                                                              -35  -13   +13.5 +41   +70.5                                                                              22      26.5    27.5    29.5                   414                                                                              -49.5                                                                              -24   +0.5  +23   +49  25.5    24.5    23.5    26.5                   423                                                                              -54.5                                                                              -33   -8.5  +17.5 +44  21.5    24.5    26      26.5                   DATA FOR PRIOR ART ELECTRODE (EXAMPLE 9)                                       1 -27  -16.5 +7.5  +34.5  N/A.sup.1                                                                         10.5    24.5    29.5    N/A                     9 -23  -10.5 +13   +40   N/A  12.5    23.5    27.5    N/A                     10                                                                              +79  +92.5 +115.5                                                                              +141.5                                                                              N/A  13      24      26      N/A                    104                                                                              +10  +9    +11   N/A   N/A  1       2       N/A     N/A                    DATA FOR PRIOR ART ELECTRODE (EXAMPLE 10)                                      1 -47.5                                                                              -30   -2    +28   +59  17.5    28      30      31                      49                                                                              -54.5                                                                              -33   -8.5  +17.5 +44  21.5    29.5    26.5    29.5                   110                                                                              -45  -30.5 -1    +27   +57  14.5    29.5    28      30                     181                                                                              -42.5                                                                              -23.5 +8.5  +35   +65  19      32      26.5    30                     __________________________________________________________________________     .sup.1 N/A denotes not available.                                             .sup.2 Data indicates that electrode failure occurred some time between       the 10th day and the 104th day.                                          

The electrode within the scope of the instant invention was periodicallyevaluated over a fourteen month span including continuous use during athree month period therein. Although the activity of the electrodedeclined from its earlier performance, the electrode still exhibitedsuitable performance thereby enabling its continued use beyond the firstfourteen month period.

EXAMPLE 9

A prior art Orion Research, Inc. 93-20 brand calcium electrode(hereinafter referred to as Y) was evaluated for Nernstian activity andthe data obtained therefrom is also set forth in Table I.

In addition to an unsatisfactory span per decade in the 10⁻⁵ --10⁻⁴ M/lrange, calcium electrode Y failed to respond to changes in calciumconcentration less than 4 months after intermittent use.

EXAMPLE 10

A prior art HNU System, Inc. ISE 20-20-00 brand calcium electrode(hereinafter referred to as Z) was evaluated for Nernstian activity andthe data obtained therefrom is also set forth in Table I.

Although it exhibited a satisfactory span per decade response over mostcalcium concentration ranges, calcium electrode Z exhibited anunsatisfactory span per decade in the 10⁻⁵ -10⁻⁴ M/l range. Thisshortcoming is significant in that an electrode must exhibit a suitablespan in this low concentration range if it is to be suitable for usewhen microsampling is required, e.g., in medical diagnostic areas suchas the diagnosis of premature infants.

Another shortcoming of calcium electrode Z is its slow and non-steadyresponse to calcium concentrations. This fact can be seen in FIG. 5which is a copy of a chart recording of calcium electrode Z for variouscalcium concentrations. The chart speed was 0.5 inch per minute. FIG. 5graphically depicts the failure of electrode Z to reach a steady stateat any of the 5 calcium concentrations tested even after a lapse ofseveral minutes at each calcium concentration, thereby making itdifficult for one to obtain a precise quantitative answer.

In sharp contrast, FIG. 6 depicts a chart recording of an electrode(prepared in Example 7 and evaluated for Nernstian activity in Example8) within the scope of the instant invention. The chart speed was also0.5 inches per minute. FIG. 6 graphically depicts the fact thatelectrodes within the scope of the instant invention quickly (i.e.,within a few seconds) reach and hold a steady state at each of the 5calcium concentrations tested. This property makes the electrodes of theinstant invention highly suitable for use in automated equipment whereinit is essential to quickly arrive at a steady state. Furthermore, oneusing an electrode within the scope of the instant invention would alsohave a higher confidence level in the accuracy of the data obtainedtherefrom because of the lack of drift present in the electrode.

Based on this disclosure, many other modifications and ramificationswill naturally suggest themselves to those skilled in the art ofion-selective electrodes. These are intended to be comprehended aswithin the scope of this invention.

BIBLIOGRAPHY

1. Koryta, Analytica Chimica Acta, 61:329-411 (1972).

2. Buck, Analytical Chemistry, 46(5):28R-51R (1974).

3. Koryta, Analytical Chimica Acta, 91:1-85 (1977).

4. Buck, Analytical Chemistry, 50(5):17R-29R (1978).

5. U.S. Pat. No. 3,429,785.

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10. U.S. Pat. No. 3,932,233.

11. Moody et al., Analyst, 95:910-918 (1970).

12. Cattrall et al., Analyticali Chemistry, 43(13):1905-1906 (1971).

13. Griffiths et al., Analyst, 97:420-427 (1972).

14. Subryan et al., Clinical Chemitry, 18(12):1459-1462 (1972).

15. Ruzicka et al., Analytica Chimica Acta, 67:155-178 (1973).

16. Morf et al., Analytical Letters, 7(1):9-22 (1974).

17. Thomas, Proc. Soc. Analyt. Chem., 340-342 (December, 1974).

18. Pretsch et al., Research Development, 20-24 (March, 1974).

19. Cattrall et al., Analytica Chimica Acta, 76:269-277 (1975).

20. Schwartz, Clinica Chimica Acta, 64:227-239 (1975).

21. Ammann et al., Analyticali Letters, 8(10):709-720 (1975).

22. Fuchs et al., Clinica Chimica Acta, 67:99-102 (1976).

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The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A compound having aformula ##STR7## wherein each X and Y is an alkyl(aryl), radical whereinsaid alkyl moiety consists of 1-12 carbon atoms; and said aryl moietyconsists of 6, 10, 12 or 14 carbon atoms; andZ is selected from a groupconsisting of alkyl radicals containing 1-12 carbon atoms; alkenyl andalkynyl radicals containing 4-12 carbon atoms; and cycloalkyl andcycloalkenyl radicals containing 6 to 12 carbon atoms.
 2. The compoundof claim 1 wherein X and Y are the same.
 3. The compound of claim 2wherein X and Y are selected from the group consisting of(t-butyl)phenyl, (t-butyl)diphenyl, (t-butyl)naphthyl, (n-octyl)phenyl,(iso-octyl)phenyl, (t-octyl)phenyl, (t-octyl)naphthyl, (methyl)phenyl,(ethyl)phenyl, (n-propyl)phenyl, (isopropyl)phenyl, (n-butyl)phenyl,(iso-butyl)phenyl, (n-pentyl)phenyl, (n-hexyl)phenyl,(1,2-dimethylbutyl)phenyl, (2-ethylhexyl)phenyl, (iso-nonyl)phenyl,(n-decyl)phenyl, (iso-decyl)phenyl, and (n-dodecyl)phenyl.
 4. Thecompound of claim 3 wherein X and Y are selected from the groupconsisting of p-(1,1,3,3-tetramethylbutyl)phenyl, p-(iso-decyl)phenyl,p-(n-decyl)phenyl, p-(2-ethylhexyl)phenyl, and p-(n-octyl)phenyl.
 5. Thecompound of claim 1, 2, 3 or 4 wherein Z is selected from a groupconsisting of cyclohexyl, cyclooctyl, cyclooctenyl, octenyl-1,cyclododecyl, dodecenyl-1, t-butyl, n-octyl, t-octyl, methyl, ethyl,n-propyl, iso-propyl, n-butyl, 3-butenyl, sec-butyl, n-pentyl, n-hexyl,1-heptynyl, 1-2,di-methylbutyl, 2-ethylhexyl, n-decyl, and n-dodecyl. 6.The compound of claim 1, 2, 3 or 4 wherein Z is ethyl.
 7. The compoundof claim 1, 2, 3 or 4 wherein Z is methyl.